A dry type transformer uses a complex system of air and solid insulation to prevent energized parts from contacting each other or ground. Many dry type cast coil transformers, such as disclosed in U.S. Pat. No. 6,445,269, are filled with epoxy in a horizontal orientation which makes a flat top surface called a ‘dome’. The dome area of a transformer houses the start and finish taps as well as voltage adjustment taps that have a large voltage gradient. This voltage gradient can cause solid insulations to electrically track due to material properties and distance. This dome area is where the customer makes connections to the transformer and where the voltage input/output of the transformer is adjusted to account for the incoming utility voltage. One of the main considerations is the track path from an energized part to another conductive part at a different potential. The flat top surface of the conventional dome area can lead to medium voltage tracking between energized parts when exposed to harsh environments such as off shore platforms, refineries, wind turbines, pulp and paper mills, etc.
Conventionally, increasing the track path requires the transformer coil to be cast with the voltage adjustment taps oriented downwardly or vertically to create bushings. Such a transformer coil has two common disadvantages. First, more epoxy is used than actually needed to fulfill the requirements of the coil. Secondly, the regions of the unnecessary epoxy are prone to the risk of cracks because of the large thickness of epoxy.
Thus, there is a need to provide a dome structure for a dry type cast coil transformer with undulation structure that allows a greater track path between taps, allows a casting process where the voltage taps face upwardly, and uses less epoxy than conventional dome areas.